1. Field of the Invention
The present invention relates to video-tape recording and reproducing apparatus, and more particularly to video-tape recording and reproducing apparatus which can record and reproduce, via a fixed multi-channel magnetic head, multi-channel transformer signals obtained from field signals by the use of the Hadamard Transformation System or the Time-Sharing System; and especially which can cancel out cross talk current caused by interference between heads during recording.
2. Description of Prior Art
Formerly, because of the special differential characteristics of recording and reproduction by magnetic heads used in this kind of video-tape recording and reproduction apparatus, the recording and reproduction of direct current components, which a transformer signal includes, has been difficult. Normally, the transformer signal is used to frequency modulate a charrier wave, so that the modulated carrier wave can be recorded and reproduced.
But if a multi-channel head is used as the magnetic head, interference occurs between the magnetic heads, caused by the close proximity of modulated carrier waves to each other, so that in addition to the recording current which passes through the head, an interference current (hereinafter called the cross talk current) is also present, and is recorded by the magnetic tape. If the cross talk current is recorded, on reproduction a beat type noise is produced by a combination of the recording current carrier wave frequency and the cross talk current carrier wave frequency.
FIG. 1 shows an FM modulated and demodulated frequency spectrum, and an explanation follows of the occurence of beat noise when cross talk current is reproduced. In FIG. 1, J.sub.0, +J.sub.1, +J.sub.2, -J.sub.1, -J.sub.2, represents the FM modulated recorded current frequency spectrum, and J.sub.c0, +J.sub.c1, +J.sub.c2, -J.sub.c2, represents the cross talk current spectrum. Also, the hatched area represents the FM modulated passing zone on reproduction. Therefore, if the lower frequency bands (-J.sub.1, -J.sub.2, -J.sub.3) drop into this zone, a beat disturbance will be created. Generally, the FM carrier wave frequency is chosen to be above that of the upper frequency limit of the above-mentioned passing zone. However, if a cross talk current exists, the difference in the carrier waves, i.e., in FIG. 1 among components such as J.sub.c0 -J.sub.0, J.sub.c1 -J.sub.1 and J.sub.c2 -J.sub.2, creates lower frequency band components which drop into the demodulated passing zone, so it is very difficult to avoid beat noise. One method of eliminating such noise might be to make a large frequency differential between J.sub.0 and J.sub.c0 in order that the lower frequency band values of J.sub.c0 -J.sub.0, J.sub.c1 -J.sub.1, J.sub.c2 -J.sub.2 become greater than the passing zone frequency and this is limited by the frequency band capacity of magnetic transformer parts.